A graphene sheet, which is, as carbon nanotube, a novel carbon material that exhibits quantized conduction (ballistic conduction), and is attracting attention as a revolutionary low-resistance interconnect as an alternative to metal interconnects. Because the average mean free path of the electrons in a graphene sheet is great, being about 100 nm to about 1 μm, the graphene sheet is, in terms of electrical conduction, highly advantageous for long distance interconnection. A graphene sheet is formed by a thermal reaction between a catalytic metal layer and a carbon layer. But, there has been a problem that the conductivity of a graphene sheet decreases to approximately a half when a catalytic metal is brought into contact with the surface of the graphene sheet. Under these circumstances, there is a demand for a graphene sheet having a lower resistance.